graph Pattern
13 problems
Pattern pages help build reusable solving frames. Identify signals first, then explain state, transition, and edge handling.
Recognition Signals
- Look for nodes with no incoming edges as a hint for mandatory inclusion.
- Consider in-degree counting to avoid full traversal of the DAG.
- The hint about thinking in reverse is a strong signal to identify which color could have been printed last.
Solve Flow
- 1. Define the active state/window.
- 2. Update state while preserving invariants.
- 3. Validate with edge-heavy examples.
Common Misses
- Assuming any node can be included without checking in-degree may lead to non-minimal sets.
- Adding dependencies in the wrong direction is the most common bug; if color d appears inside color c's rectangle, then c must come before d.
- Double-counting a road that connects both cities when calculating network rank.
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